1. Field of the Invention
The present invention relates to a cooling fan failure detection apparatus for detecting failure of a cooling fan provided for cooling a battery in a hybrid vehicle.
2. Description of the Related Art
Conventionally, hybrid vehicles which carry motors as power sources for driving the vehicles in addition to engines are known. Hybrid vehicles are divided into series hybrid vehicles and parallel hybrid vehicles. In the series hybrid vehicles, the engine drives a generator whose electric power output is used to drive the motor, which in turn drives the wheels. In this case, because the output of the engine is not mechanically connected to the driving wheels, the engine can be constantly driven within an engine-speed range of a high fuel mileage and a low emissions level. Therefore, the series hybrid vehicles can achieve lower fuel consumption and lower emissions levels than conventional engine vehicles.
In contrast, in the parallel hybrid vehicles, a motor is mechanically coupled to an engine so as to assist the rotation of the drive shaft of the engine. The motor can also act as a power generator to generate electrical power, and the generated electrical energy is stored in a battery. The electrical energy charged in the battery can be supplied to electrical equipment and the like in the vehicle.
In this case, although the output of the engine is mechanically connected to the driving wheels, drive loads on the engine can be reduced. Therefore, the parallel hybrid vehicles can also achieve lower fuel consumption and lower emissions levels than conventional engine vehicles.
The parallel hybrid vehicles can be divided into several types. One is a type in which a motor is connected to an output shaft of an engine so that the motor can assist the output of the engine, and when, for example, the vehicle decelerates, the motor acts as a generator to charge a battery or the like. Another is a type in which both or either of a motor and an engine can generate driving force, and a generator is independently provided.
These hybrid vehicles perform various controls, for example, when the vehicle accelerates, the motor assists the output of the engine, and when the vehicle decelerates, the motor generates electric power by deceleration regeneration to charge a battery or the like. Therefore, it is possible to constantly maintain electrical energy (the remaining battery charge) in the battery and to respond to demands by the driver of the vehicle.
It is well known that the charging efficiency of batteries used in hybrid vehicles is suddenly degraded when the temperature of the battery reaches a certain temperature. The temperature at which the charging efficiency is degraded depends on the performance of the battery. If charging of a battery is performed when the temperature of the battery is higher than the critical temperature, most of the charging energy is merely converted to heat, and the supplied electric energy cannot be stored in the battery. Furthermore, if charging or discharging of the battery is performed when the temperature of the battery is higher than the critical temperature, the temperature of the battery is further elevated, and the risk arises that the battery will deteriorate. Therefore, in a hybrid vehicle, a cooling fan is attached to the battery for cooling the battery so as to maintain the temperature of the battery under the temperature above which the charging efficiency is suddenly degraded.
However, if charging or discharging of a battery is performed when the driver of the hybrid vehicle does not notice the failure of the cooling fan, the temperature of the battery is unduly elevated, and deterioration of the battery may be accelerated. In order to prevent such a problem, it is necessary to detect the failure of the cooling fan in advance.
However, in order to detect the failure of the cooling fan, it is necessary to provide a sensor for detecting abnormality and a signal processing circuit for determining whether the cooling is failing or the like, and there arise problems such as increases in the manufacturing cost and the body weight of the hybrid vehicle. Furthermore, when the cooling capacity of a cooling fan is degraded due to blocking of the inlet or outlet of the cooling air passage, it is difficult to detect such a degradation of the cooling capacity by a simple electric method such as detection of the breaking of a wire or a short circuit.
The object of the present invention is to provide a cooling fan failure detection apparatus which can detect a failure of a cooling fan without using an additional sensor or an additional signal processing circuit.
In order to achieve the above object, a cooling fan failure detection apparatus of the present invention comprises a cooling capacity calculation device (temperature difference calculation unit 62 in the embodiment) which calculates a cooling capacity of a cooling fan provided in the hybrid vehicle; a battery heating value calculation device (input/output electric power calculation unit 61 in the embodiment) which calculates a heating value of a battery provided in the hybrid vehicle; an assumed temperature change calculating device (assumed temperature change calculation unit 63 in the embodiment) which calculates an assumed temperature change of the battery based on the heating value and the cooling capacity; an actual temperature change calculating device (actual temperature change calculation unit 64 in the embodiment) which calculates an actual temperature change of the battery; and a failure determination device (failure determination unit 66 in the embodiment) which determines whether the cooling fan is failing by comparing the assumed temperature change calculated by the assumed temperature change calculating device and the actual temperature change calculated by the actual temperature change calculating device.
Moreover, a hybrid vehicle of the present invention comprises an engine which outputs a driving force for the hybrid vehicle; a motor which outputs an assistant driving force so as to assist the driving force of the engine; a battery which supplies electric power to the motor when the assistant driving force is necessary, and which stores electric power generated by the motor when the assistant driving force is not necessary; a cooling fan which cools the battery; a cooling capacity calculation device which calculates a cooling capacity of a cooling fan provided in the hybrid vehicle; a battery heating value calculation device which calculates a heating value of a battery provided in the hybrid vehicle; an assumed temperature change calculating device which calculates an assumed temperature change of the battery based on the heating value and the cooling capacity; an actual temperature change calculating device which calculates an actual temperature change of the battery; and a failure determination device which determines whether the cooling fan is failing by comparing the assumed temperature change calculated by the assumed temperature change calculating device and the actual temperature change calculated by the actual temperature change calculating device.
According to the present invention, failure detection of the cooling fan is performed using outputs only from sensors which have been already provided for calculating the remaining battery charge in a battery control apparatus. Therefore, without providing additional dedicated sensors or the like, a failure detection of the cooling fan is possible, and increases in the manufacturing cost and the body weight of the hybrid vehicle can be prevented.
Furthermore, because this apparatus detects a failure of the cooling fan based on a change in the temperature of the battery, even if the cooling capacity of the cooling fan is degraded due to blocking of the inlet or outlet of the cooling air passage, it is possible to detect such a degradation of the cooling capacity.